Double sided probing structures

ABSTRACT

A test configuration for double sided probing of a device under test includes a holder to secure the device under test in a first orientation, a calibration substrate secured in a second orientation and a probe capable of calibration using the calibration substrate and probing the device under test.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/609,605, filed Sep. 13, 2004.

BACKGROUND OF THE INVENTION

The present application relates to probing.

Characterizing the actual performance of high speed integrated circuit based systems requires accurate knowledge of the electrical characteristics of the wafer forming the integrated circuit, characteristics of the integrated circuit itself, characteristics of the package into which the integrated circuit is placed, characteristics of the circuit board or support upon which the integrated circuit is supported, and characteristics of the interconnect structures which interface both the integrated circuit with the package and the package with the circuit board. These electrical characteristics, which are frequently the subject of measurement, include cross-coupling with neighboring lines, spectral dispersion, electrical resonances, and loss by radiation into the surrounding dielectric.

Traditional measuring stations are constructed to support a device under test, such as an integrated circuit board or package, in a horizontal position. This arrangement provides direct physical access to the probing device from only a single side of the package. Simultaneous access to both sides of a circuit board or package is accordingly unavailable in such test structures. Specially constructed mounting cards are sometimes used which not only hold a package but also attempt to provide all connections on the top of the card for physical access to probing. The use of package mounting cards introduce effects into the measurement data which are not due to the package or its interconnects. These effects must, themselves, be determined and either compensated for or modeled into the final analysis of the data. Regardless, of how these effects are handled, they degrade both the efficiency and accuracy of the resulting package electrical characterization.

GigaTest Labs provides a GTL 5050 Probe Station that facilitates probing on opposite sides of a printed circuit board. A calibration substrate is supported in a horizontal orientation by the horizontal support. The probes are supported by the horizontal support and aligned in an opposing relationship with respect to the calibration substrate. Thereafter, the probes are calibrated using the calibration substrate to determine calibration parameters, such as a set of S parameters. The calibration parameters are used in further measurements to calibrate primarily for the effects of the cables and probe so that the characteristics of the device under test can be determined. One of the clamps is then clamped to the horizontal support of the station in a position suitable for testing one side of the circuit board. The horizontal support including the clamped probe is then flipped over. The other clamp is then clamped to the now upper side of the horizontal support of the station in a position suitable for testing the other side of the circuit board. While functional, the significant movement of the probes necessary for positioning and the flipping of the table necessitates long cables, which introduce error into the calibration.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a horizontal calibration substrate and a vertical device under test.

FIG. 2 illustrates a probe positioner.

FIG. 3 illustrates the probe positioner of FIG. 2 in a different orientation.

FIG. 4 illustrates a horizontal calibration substrate and a horizontal device under test.

FIG. 5 illustrates a vertical calibration substrate and a vertical device under test.

FIG. 6 illustrates a vertical calibration substrate and a horizontal device under test.

FIG. 7 illustrates a lateral plate assembly interconnected to a guard potential.

FIG. 8 illustrates a pair of plate assemblies interconnected to a guard potential.

FIG. 9 illustrates a vertical sliding plate assembly interconnected (both sides of device under test) to a guard potential.

FIG. 10A-NN illustrate further embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The present inventors considered the available dual sided probing solutions and came to the realization that a probing solution that permits dual sided probing with minimal reconfiguration of the probe station would be advantageous for increasing the probing efficiency while simultaneously increasing calibration accuracy. Referring to FIG. 1 as an initial matter it was determined that the device under test 30 is preferably supported by a holder 10 that is in a vertical orientation, such as substantially 90 degrees with respect to a horizontal support 20. The device under test 30, may include any suitable device, such as for example, pogo-pin contactors, grid ball array package I/Os and vias, test sockets, via arrays, printed circuit boards, and thru paths of transmission lines that traverse right-angle board to board connectors. In addition, a differential impedance test may be performed. The vertical orientation of the device under test 30 reduces the size of the probing system and permits effective use of a microscope 40 to view both sides of the device under test 30.

In order to perform calibrated tests, the probing system includes a substrate support 50 for a calibration substrate 60. The calibration substrate includes one or more calibrated structures thereon which facilitate the calibration of one or more probes. The calibration substrate is preferably substantially parallel to the horizontal support 20. A pair of probe positioners 70 and 80 (see FIG. 2) are aligned with the calibration substrate 60. Each of the probe positioners 70 and 80 typically includes a probing element 100 and 105 which includes a respective contacting portion at the end thereof. The probing contacting portion normally includes a plurality of aligned probing contacts. Therefore, the theta of each set of probing contacts is adjusted using the theta adjustment of the probe positioner to align the probing contacts with the surface of the calibration substrate. In this manner, all of the probing contacts come into proper contact with the calibration substrate (otherwise one or more probe contacts may not make proper contact). The calibration is normally a vector calibration using a vector network analyzer.

The probe positioners 70 and 80 are then repositioned on the horizontal support 20 in a position proximate each side of the device under test 30. A stand 72 (or multiple stands) may be used, if desired. While some existing probes may permit the re-orientation of the probing contacts to a different position, it takes significant time to adjust the orientation of the probing contacts sufficiently in line with the device under test 30 for successful probing. In addition, since the adjustment from one orientation to another is normally along a continuous axis of rotation, it is problematic to sufficiently align the probing contacts with the surface of the device under test 30 so that proper probing contact is made. If the probe contacts are slightly out of alignment, then the test will either not function at all or appear to function properly but actually be providing inaccurate results. Further, if the user needs to make multiple touch downs on the same pad to properly align the probing contacts with the pads on the device under test, then there is a significant probability that the pads on the device under test will be damaged, resulting in either a damaged device under test or otherwise inaccurate measurements.

To alleviate this probe alignment limitation the present inventors came to the realization that the probe should include a structure that permits defined movement from a horizontal probing orientation to a vertical probing orientation. In this manner, the probe contacts move from a first orientation to a second orientation with certainty that the orientations have a predefined angular relationship between them, such as 90 degrees.

Referring to FIG. 2, the probe positioner 70 (80) may include a probing element 100 with contacting elements. Typically the probing element 100 includes a coaxial cable with a plurality of contacting elements connected to the end thereof. The probing element 100 is supporting by a probe support 102. The probe support 102 may be rotatably connected 106 to a support fixture 104, such as with a pin that may be tightened to secure the probe support 102 in place. This interconnection 106 provides for adjustability in the location of the probing contacts and their angular contact to the device under test.

The support fixture 104 is interconnected to a theta adjustment structure 108 that includes a knob 110 that, when turned, adjusts the theta orientation of the probing elements. The theta adjustment structure 108 is secured to a plate 110. The plate 110 includes a set of openings therein which match openings in a pivot block 112 so that the plate 110 may be secured to the pivot block 112. In FIG. 2, the probing element 100 is oriented in a horizontal orientation. In order to provide a convenient manner of adjusting the probing element 100 to a different predetermined orientation, the pivot block 112 is mounted to a hinge 114. When the user desires to change the orientation of the probing element 100, the user may remove a screw 116 which permits the pivot block 112 to pivot around the hinge 114 to a second position where the pin 116 is replaced to secure the pivot block 112 in a fixed position, as illustrated in FIG. 3. The result of removing the pin 116 and pivoting the pivot block 112, is to change the orientation of the probing element 100 by a predetermined angle, such as 90 degrees. Other fixed positional movements may likewise be used depending on the particular application and orientation of different portions of the probe station.

With the probing element 100 oriented in a vertical direction, as illustrated in FIG. 3, the probe is suitable for being calibrated on a calibration substrate that is in a horizontal orientation. The contacting members may be properly adjusted to achieve a uniform contact with the calibration substrate. Thereafter, the probe may be readily modified to a horizontal orientation using the hinge 114 with a 90 degree adjustment. The device under test 30 has a vertical orientation, so the probe as illustrated in FIG. 3, after rotation, is thus in a suitable position for testing. The probe may be moved on the horizontal support 20, as necessary, to position the probing contacts near the device under test. With the 90 degree adjustment being known, which is the angular relationship between the calibration substrate 60 and the device under test 30, the probing contacts will be in the proper alignment for testing the device under test 30. In this manner, no additional adjustment of the probing contacts theta alignment is typically necessary and the pads on the device under test 30 will not likely be worn through attempting to achieve proper alignment of the probing contacts. In addition, each of the probe positioners may be rotated in a different direction so that suitable contact may be made to each side of the device under test 30.

In addition, a plurality of faces of the pivot block 112 may include a set of holes therein so that the plate 110 may be secured to different faces of the pivot block 112, as desired. In this manner, the rotation of the pivot block 112 may achieve different orientations of the probe.

The hinge 114 is affixed to another support 116. The support 116 may include a pair of opposing groves 118 and 120 defined therein. By loosening a screw 122, the support 116 may freely slide up and down the plate 124, and is secured in place by tightening the screw 122. In this manner, the height of the plate 116 may be readily adjusted. The opposing groves 118 and 120 also permit the plate 116 to be completely disengaged from the plate 124 then the plate 116 (and attached probing elements) may be rotated 90 degrees, 180 degrees, or 270 degrees, and then engaged with the plate 124 in a different orientation. This provides another manner for adjusting the orientation of the probe for alignment with a calibration substrate and a device under test.

The plate 124 is secured to an x-y-z adjustment mechanism 126 that may shift the probe by using a respective knobs 132, 130, and 128. In this manner, fine adjustments of the x-y-z orientation of the probe 100 may be performed by the user for probing the device under test.

Referring to FIG. 4, an alternative orientation is illustrated that makes effective use of the probe positioners described herein. The calibration substrate is maintained in a horizontal orientation, and the probes are calibrated. Thereafter one of the probe positioners is oriented to probe the top of the device under test, which is the same orientation of the probe as is used for calibration. The probing contacts of the other probe positioner are rotated 180 degrees, and then oriented to probe the bottom of the device under test. In this manner, the device under test may be effectively probed. Referring to FIG. 5, another alternative orientation is illustrated that makes effective use of the probe positioners described herein. The calibration substrate 60′ is maintained in a vertical orientation on the support 50′, and the probes are calibrated. Thereafter one of the probe positioners is oriented to probe the side of the device under test, which is the same orientation of the probe as is used for calibration. The probing contacts of the other probe positioner are rotated 180 degrees, and then oriented to probe the other side of the device under test. In this manner, the device under test may be effectively probed.

Referring to FIG. 6, another alternative orientation is illustrated that makes effective use of the probe positioners described herein. The calibration substrate 60″ is maintained in a vertical orientation on the support 50″, and the probes are calibrated. Thereafter one of the probe positioners is oriented to probe the top of the device under test. The probing contacts of the other probe positioner are rotated and then oriented to probe the other side of the device under test. In this manner, the device under test may be effectively probed.

It is to be understood, that depending on the orientation of the probe positioners including the probing element, calibration substrate, and the device under test with respect to one another together with respect to the orientation of the probe positioners when positioned for subsequent probing, the modification of the orientation of the probing element (if modified) may change.

Traditionally, the measurements used to simultaneously test two sides of a vertically oriented structure have been sufficient to obtain desirable results. However, in the case of attempting to characterize especially low noise characteristics it has been determined that the noise levels, in some cases, are to large. In such a case it has been determined that the addition of guarding structures around the vertically oriented probing device would be advantageous. The guarding structures are conductive members that are provided with a potential that tracks, or otherwise approximates, the potential in the signal path. In this manner, the leakage from the signal path is reduced. Referring to FIG. 7, a modified vertical support structure includes an exterior ring 200 that is provided with a guard potential of a signal path. The exterior of the ring is preferably insulated from other conductive members. In addition, the exterior ring preferably encircles a majority of the device under test on one or more sides of the device under test. Referring to FIG. 8, for one or both of the exterior surfaces of the device under test a conductive plate assembly 210 may be provided, within which the probes test the device under test, and each of the conductive plates may be connected to a guard potential of a signal path. For example, the potential of the conductive plate proximate the respective probe may be interconnected to a guard representative of the signal path of the respective probe.

Referring to FIG. 9, a modified structure includes a set of vertically oriented interconnected slidable plates 230 that define an opening 240 therein through which the probe tests the device under test. The plates 230 may be provided on one or both sides of the device under test. The opening 240 may shift such that other regions of the device under test may be tested. In this manner, the device under test has a significant region that is of a guard potential.

Referring to FIGS. 10A-NN, other embodiments are illustrated.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow. 

1. A test configuration comprising: (a) a holder for a device under test in a first orientation; (b) a calibration substrate in a second orientation; and (c) a probe capable of calibration using the substrate and probing the device under test. 